Various challenges are encountered when designing pipe elements to be joined by mechanical pipe couplings. Such couplings comprise two or more coupling segments joined in end to end relation by threaded fasteners. The segments surround a central space which receives the pipe elements. Each segment has a pair of arcuate projections known as “keys” which engage the outer surfaces of the pipe elements. The keys are often received in circumferential grooves in the pipe elements which provide a positive mechanical engagement against bending and axial loads applied to the joint. Each segment also defines a channel between its pair of arcuate projections which receives a ring-shaped gasket. The gasket is typically compressed between the segments and the pipe elements to effect a fluid tight joint.
Circumferential grooves are advantageously formed by cold working the sidewall of the pipe element because, unlike cut grooves, material is not removed from the pipe sidewall and thus thinner walled pipe elements may be grooved by the cold working process. It is advantageous to use thinner walled pipe elements for weight and cost savings in high pressure and/or high load applications. However, prior art cold working methods and pipe designs do not produce coupling and pipe element engagement features adequate for high loads and pressures sustainable by comparable cut groove systems used on thicker walled pipe elements. There are clear advantages to be had through improvements to the design and manufacture of thin walled grooved pipe elements by cold working which will allow thin walled grooved pipe elements to be joined by mechanical couplings and used in high pressure/high load applications.